Telephone.



K0 MODEL.

PATENTED APR. 5, 1904. J. TROWBRIDGE.

TELEPHONE. APPLIUATION FILED MAY 18, 1903.

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No. 756,437. PATENTED APR. 5, 1904.

J. TROWBRIDGE.

TELEPHONE.

APPLICATION FILED MAY 13, 1903.

H0 MODEL.

sums-4:11am a.

w a I I a s UNITED STATES Patented April 5, 1 904.

JOHN TROWBRIDGE, OF CAMBRIDGE, MASSACHUSETTS.

TELEPHONE.

SPECIFICATION forming part of Letters Patent No. 756,437, dated April 5,1904. Application filed May 18, 1903. Serial No. 157,561. (No model.)

To all whom it may concern.-

Be it known thatI, JOHN TROWBRIDGE, a citizen of the United States, anda resident of Cambridge, in the county of Middlesex and State ofMassachusetts, have invented new and usefulImprovements in Telephones,of which the following is a specification.

The object of my invention is to relay or repeat telephonic currentundulations in such manner that relatively feeble undulations in onetelephone line will be reproduced in another line with enhanced forceand amplitude and without impairment of the essential telephoniccharacter of the current undulations and consequent deterioration ofarticulation and to provide such a relay apparatus that the telephonicsystem as a whole, including relays, .will reciprocatethat is to say,will transmit speech-messages electrically in either direction, as inthe case of the ordinary continuous line.

In United States Letters Patent to Samuel Sheldon and myself, No.407,799, dated July 30, 1889, there is described a device whereof thepurpose was to utilize powerful electrodynamic currents to energizemagnets in a relay apparatus. This apparatus was also intended for useas a receiving instrument. As the continuous current generated by adynamo involves the employment of a commutator, there is set up in thecurrent a rapidly-recurring series of pulsations or throbs due to theaction of the commutator, and, as was pointed out in the said Patent No.407,799, the inductive pulsations produced by the commutator wherever anarmature-coil is employed which intersects the lines of force of thesurrounding magnetic field (such as illustrated by Siemenss Patent No.149,797, dated April 14, 1874) will, if the armature be employed as partof a telephonic system, overpower the more delicate undulationscharacteristic of a telephonic current. Consequently, as thespecification of the Trowbridge and Sheldon Patent No. 407,799 setsforth in detail, the object was to arrange an armature wound andsuspended in the field of a dynamo-currenteXcited electromagnet in suchmanner as to elude the disturbing commutator influences, and thus becapable of transmitting speech as a relay or as a receiver.Unfortunately for the practical accomplishment of this purpose, thehypothesis of the said Patent No.407 .7 99 failed to take account ofother factors, both electromagnetic and mechanical, and consequently theapparatus as a whole, although it obviated the difficulties due tocommutator disturbances, failed satisfactorily to transmit theelectrical undulations characteristic of and essential to the productionof articulate-speech sounds. The net failure of the said apparatus maybe correctly characterized thus: The instrument of Patent No. 407,799,whether used as a relay or as a receiver, was incapable of transmittingthrough its several transforming members, unimpaired and constant incharacter, the telephonic undulations of the incoming line. Theundulations emitted by the instrument were more or less confused withdisturbing undulations superposed upon the correctly-modulatedincomingwaves or pulsations, so that when finally transformed intosound-waves they lost, in whole or in part, the essential quality ofarticulate speech. This imperfection was usually manifested by confusedbuzzing or rattling sounds, which always interfered with and oftendestroyed the pure essential articulate-speech sounds. The Patent No.407,799, however, setforth a mode of enhancing or amplifying the feebleundulations of a nearly-exhausted telephonic current by converting theundulations thereof into magnetic undulations within a supplementalmagnetic field, although, as I have pointed out and, as experienceproved, the mode of accomplishing'this result shown in the said patentfailed to take account of many then unsuspected conditions, and thusfailed to produce the useful result of transmittingand forwarding withunimpaired articulation the undulations of the incoming current. I

I have discovered the electrical and mechanical causes of the defects ofthe instruments described in Patent No. 407,799 and have by my presentinvention herein set forth proa second line, thus preserving the exactun:

dulatory correspondence with the sound-waves of articulate speech.

My invention consists of a novel method of repeating electricalundulations and also of an apparatus which employs my new method totransmit and repeat telephonic messages. In an application for UnitedStates Letters Patent, Serial No. 157,560, filed concurrently herewith Ihave set forth and claimed my said method. and I therefore wish it to beunderstood that while this specification for the purpose of explanationinvolves a description of my methodI reserve the same in whole and partfor claim in the said concurrent application.

In the drawings hereto annexed, Figure 1 is a plan view, partlydiagrammatic and conventional, of a telephonic repeating instrument orrelay embodying my invention. Fig. 2 is a diagram of a completetelephone-line with a single reciprocating relay 1 station. Fig. 3 is adiagram of a non-reciprocating telephone-line with two relays arrangedtandem. Fig- 4: is a diagram of a reciprocating tandem relay-line, andFigs. 5 and 6 show other forms of repeating instruments or relays.

Referring to Fig. 1, upon a suitable base and by means of brackets M Mare mounted a pair of horseshoe-magnets M M. These may be permanentmagnets or electrom agnets. In the latter case they should be energizedby a continuous and steady current, as from a primary or storagebattery. Likewise mounted on the base is a telephonic transmitter T,which is here shown as a solid-back carbon-button transmitter. mountedon the impulse-receiving member of the transmitter T, as by a stem P,there is an armature A, which is preferably composed of soft-iron rodsor short wires. At the ends of the armature A are secured transversepolepieces a a, likewise of softiron. I have found by experiment thatthese pole-pieces while not essential to the performance of my inventionnevertheless increase the responsive delicacy of the instrument. rangedwith their north and south poles N S mutually opposite each other, or,in other.

words, the north poles of the magnets M M are diagonally opposite, asalso are the south poles. armature pole-pieces cm is as shown in Fig. 1by the letters -n s. Adjusting-screws M enable the-operator to adjustthe magnet-poles N S as close as desired tothe armature pole- -pieces.These screws should be of brass or other diamagnetic material. Themagnets M M should be of equal strength, so as to maintain substantialequilibrium in the field and with respect to the armature A.

The mode of mounting the magnets M M in polar opposition, as shown,establishes a field which may be described as quadrilateral andsymmetrical or balanced, and the arma- Firmly and rigidly The magnets MM are ar- The resulting induced polarity of the.

ture A is normally in a state of equilibrium, the balanced forces of themagnetic field exerting no stress upon the impulse-receiving member ofthe transmitter T. This condition I regard as important, because thetransmitter T, whatever be its specific character,

is thus maintained in precisely the same deliv cately-responsive statethat characterizes a transmitter which is prepared in the usual andproper way for the reception of sound-waves. I have found by carefulexperiment that with an armature in an unbalanced non-symmetricalmagnetic field connected directly to a transmitte'rsay to a diaphragmtheconstant pull of the magnetic field causes a distortion of thediaphragm, and consequently produces disturbing eflects which obscurethe proper articulation of the instrument.

The incoming'telephonic line Lwe will sup- I pose to be at such adistance from the transmitting devies at its remote end that theelectrical undulations are feeble, so that reproduction of audiblespeech thereby in the usual manner is impracticable. In circuit with'theline L, I wind an armature-coil Z on the arma- .90 ture ,A, preferablybunching the coil in. two

parts near theends of thearmature, leaving the middle portionthereofbare of coil, and.

thus obtaining practically all the electromagnetic effect of the coils Zwhile saving weight.

The transmitter T is wired in the usual manner, a battery B of properstrength in its immediate circuit. In this circuit is also located theprimary of an induction-coil I, whereof the secondary is in the outgoingor relay line It.

When the incoming line L is quiet and no electrical undulations arepassing on it, the

relay instrument is in equilibrium; but when electrical undulations areset up in this line the polarity of the armature A is varied in exactcorrespondence and consonance with the electrical undulations in theline L, and anundulating or vibrating magnetic field is generated in thefield of the magnets M. The resulting effect is the product of thearmaturecoil eifects and the balanced-field effect, and the magnetic,and consequently the mechanical, results are enhanced and amplified.Within quite generous limits the strength of the balancedmagneticfieldmay be raised and the consequent product effects increased.

vIOO

Moreover, by means of the polar relationship of the field and armaturecoil all torsional moments are in equilibrium and theresultantmechanical vibrations are in a straight line and are exerted inthis straight line perpendicularly to the impulse-receiving member ofthe transmitter T and perpendicularly to the planes of contact betweenthe resistancevarying members of the transmitter. This same rectilineartransmission of mechanical effects and perpendicular impact may readilybe secured whatever be the structural character of the transmitter. Bypreserving these conditions the relay or repeating instrument sends tothe outgoing or relay line R undulations precisely corresponding to theincoming undulations of the line L, which excite the armature-coil Z andbring into action the vibration-amplifying forces of the balanced fieldof the magnets M. Thus the transmitter T is impressed with amplifiedundulating impulses, which are essentially the same in articulatecharacter as the sound-waves which excited the sending instrument at theremote end of the line L, and consequently transmits to the line Runimpaired in articulate quality amplified undistorted undulationsessential to the production of intelligible articulate speech, which maythen be made manifest by a proper telephonic receiver at the remote endof the line R.

The relay or amplifying effect sensible at the receiver end of the lineR is due to several conditions-first, the product magneticamplifications of the armature-coil undulations by means of the balancedmagnetic field, whereby the mechanical impress upon the transmitter T isemphasized; second, to the relay-battery B, which supplies freshelectrical energy for transmission of undulations along the line R, and,third, to the preserva: tion and transmission, unimpaired and unobscuredand undistorted by extraneous influences, of the undulatoryarticulations of the original telephonic current.

In Fig. 2 there is illustrated by diagram an arrangement for obtainingreciprocal relay effects between two distant stations. At one station islocated the usual transmitter T, with battery B and the primary of theinductioncoil I in its circuit. The line L, including the secondary ofthe induction-coil I, armature-coil at A, the secondary of theinductioncoil 2, and the receiver R, leads to the relaystation. At thisrelay-station two instruments similar to that shown in Fig. 1 and abovedescribed are set up, the instrument M M A T in adjustment to receiveand repeat impulses from transmitter T and the instrument m m at toreceive and repeat impuses from transmitter T, which is at the end ofthe line remote from transmitter T.

ranged as follows: The same circuit R includes the two transmitters T t,the relaybattery B, and the primaries of the inductioncoils I and 2'. Atthe station remote from the instruments T and R are located thetransmitter T with the battery B and the primary of the induction-coil Iin circuit. The line L includes the secondary of the inductioncoil I thereceiver R armature-coil a, and the secondary of induction-coil I. Theoperation of this system is as follows:

Speech vibrations stimulate current undulations in the primary of coil 1and generate corresponding undulations in the line L.

The two relay instruments at the relay-station are ar- These electricalundulations are converted into magnetic undulations at the armature coilA, and these again are supplemented by reciprocal magnetic effects ofthe balanced field of magnets M M. As above described in connection withFig. 1 these reinforced magnetic undulations are reconverted intoelectrical undulations precisely corresponding to the original speechvibrations at the transmitter T, and these undulations in circuit R setup corresponding undulations in the circuit L which are in the usualmanner finally re converted into sound-waves at the receiver R where thespeech delivered at transmitter T is reproduced.

The current undulations of the circuit L passing through the secondaryof the coil 2' produce in its primary no sensible effect. Thus theresistance to the transmission of undulatory effects backward, as we maysay, through the relay instrument m 222 a t is practically prohibitory.

When the speech is made at transmitter T the reciprocal effect isperfect. The relay m m a it receives, amplifies, and transmits theundulations to the line L through the inductioncoil 2', and the receiverR reconverts them into speech. Whatever be the source of undulations,the effective relay instrument takes the message and repeats it, onerelay Works in one direction and the other in the opposite direction,and each automatically to the exclusion of the other. The practicalresults, therefore, which appeal to the users of the instruments at theends of the line are the same as if they were conversing over a simpletelephone-line short enough to render the direct communicatingundulatory current effect- The preservation of the exact articulatecharacter of the undulatory current which is peculiar to my method ofrepeating enables one to use several relays like that shown in Fig. 1 orrelay-stations like that shown in Fig. 2 in tandem. I illustrate asimple nonreciprocating tandem relay-line in Fig. 3. Therein theimpulses from transmitter Texcites the relay at station 1, thence the'undulatory current is passed on amplified to station 2, and thence toreceiver R.-

In Fig. 4 1' illustrate an arrangement of complete reciprocatingrelay-stations in tandem. In this system the arrangement of terminalstation T R with relation to relay-station 1 and that of terminalstation T R With relation to relay-station 2 are the same as therelations of the respective terminal stations of Fig. 2 of the relaysystem. The secondary of the induction-coil I, the armature-coil ofrelay instrument 2*, the secondary of induction-coil 2' and thearmature-coil of relay instrument 1 are in the line which stretchesbetween relay-stations 1 and 2. I have constructed a system of thischaracter inwhich the line-resistances were analogous to a line from NewYork to Chicago as between terminal T R and relay-station 1, a line fromChicago to Omaha as between relay-stations 1 and 2, and a line fromOmaha to Denver as between relay-station 2 and terminal station T R andhave maintained clear, audible, and unimpaired a conversation with anassistant over the said line, which transmitted speech reciprocally asreadily as an ordinary short telephone-line.

It will be observed that in contrast with the instrument and mode ofoperation described in Patent No. 407,7 99 I have by my presentinvention produced the following electrical, magnetic, and mechanicalconditions: Instead of converting the product effects of an armature andsurrounding field into rotary movements by means of unbalanced torsionalmagnetic product effects characteristic of the said patent I havemaintained torsional balance in magnetic effects and produced directrectilinear mechanical movements. Whereas in the instrument of PatentNo. 407,799 the curvilinear mechanical impulses of the suspendedarmature caused distortions and disturbances in the transmitter, in mypresent invention no such distortion or disturbances take place. Insteadof making contact between the armature-coil and the receiving members ofa transmitter by means of initial pressure (itself a cause of mechanicaldistortion and confusion of articulate with inarticulate electricalundulations) I have secured the armature-coil directly and rigidly tothe receiving'member of the transmitter, thus avoiding any confusingstresses and also eliminating the effect of individual non-electricvibrations of the independently-suspended armature. In short, I have bymy present invention contrived a method and apparatus whereby asymmetrical or balanced magnetic field, as an independent source ofpower, is enabled in coaction with an exciting-armature to repeatunimpaired the articulate undulations of a telephonic circuit with freshand amplified transmission impulses in a second or relay circuit,whereas by the apparatus and mode of operation shown in Patent No. 407,799 this functional result could not be obtained. Also I have by mypresent invention contrived a method and apparatus whereby thesymmetrical or balanced magnetic field in connection with anexciting-armature may be employed to directly produce the mechanicalvibrations of a receiver-diaphragm, so that the resulting sounds will beclear undistorted articulate speech free from disturbing sounds.

In solid-back microphone-transmitters now in general use the metallicdiaphragm D is, as shown in Fig. 5, rigidly clamped at its edges to acasing, on which the electrode-holder is also rigidly fixed. The stem Pis fixed rigidly at one end to the middle of the metallic diaphragm andat its opposite end to the middle two reasons.

of the usual mica diaphragm closing the end of the electrode-holder andagainst which the movable electrode of the microphone bears. This is theusual construction, and in carrying my invention into effect the'onlychange necessary to make in the microphone-transmitter as at presentconstructed is to mount the small iron armature A on the stem P betweenthe metallic and mica diaphragms and fix the two magnets M within thecasing of the transmitter properly disposed with relation to the ironarmature A.

In Fig. 6 I have shown another form of instrument, which difiers fromthat above described in that a block D of whitewood is fixed to themiddle of the metal diaphragm, and in this block D the armature A ismounted with only its two ends projecting therefrom. By thus practicallyburying the armature in the block of wood D independent vibrations ofsaid armature, which might conflict with the vibrations consonant withthe electrical undulations, are prevented, the inclosing body of woodtending to smother the same without itself being vibrated.

In telephone systems comprising a plurality of repeating instruments Ifind that it is desir able to make each adjustablethatI is, to providesome means by which the action of each instrument may be regulated so asto work in harmony with the other instruments of the system. To this endImay provide each instrument with a spring-finger d, fixed to anysuitable support and arranged to press through a block of rubber 03 uponthe side of the block D. The pressure of the spring-finger 0Z may beregulated by means of a screw 0?, by means of which the action of theinstrument may be regulated to accord with the other instruments of thesystem. The arrangement shown in Fig. 5 has the advantage of supportingthe vibrating armature A at both sides, so that the slight bendingefiect due to the weight of the armature is wholly obviated. Any supportat the side away from the transmitter T will serve for this purpose; butI prefer to employ a diaphragm clam pedat its periphery for First, thediaphragm does not tend to confuse the pure articulate vibrations of thearmature by independent tremors of its own, and, moreover, the diaphragmitself used in the manner described produces audible speech, whichenables the listening operator to detect any disturbing influences whichmay be at work, and thus to ascertain if the instrument is workingproperly to relay the message. A damping device, such as indicated inFig. 6, may be thus employed to suppress any undesirable vibrations.

With a single relay-station in line the disturbing effects due to localvibration in my relay instruments are so slight as to be negligible; butwith a tandem arrangement employing several relay-stations the localdisturbances negligible with a single station are liable to accumulateat each relay and should be suppressed.

What I claim is 1. In an instrument for repeating electricalundulations, the combination of a magnetic field, an armature-coil in aposition of balance therein, a telephonic transmitter, and connectionsarranged with relation to the reciprocal effects of the coil andmagnetic field to impart mechanical vibrations perpendicularly to thereceiving member of the transmitter.

2. Inan instrument for repeating electrical undulations, the combinationof a magnetic field, an armature-coil in a position of balance therein,a telephonic transmitter outside the balanced field, and connectionsarranged with relation to the reciprocal effects of the coil andmagnetic field to impart mechanical vibrations perpendicularly to thereceiving member of the transmitter.

3. In an instrument for repeating electrical undulations, thecombination of a magnetic field, an armature-coil in aposition ofbalance therein, a telephone-transmitter, and connections arranged withrelation to the reciprocal effects of the coil and magnetic field toimpart mechanical vibrations to the receiving member of the transmitterin a straight line.

4. In an instrument for repeating electrical undulations, thecombination of a magnetic field, an armature-coil in a position ofbalance therein wound so that the mechanical vibrations due to thereciprocal magnetic efiects of the coil and field are rectilinear, atelephonictransmitter, and connections to impart thereto the saidrectilinear mechanical vibrations.

5. In an instrument for repeating electrical undulations, thecombination of a magnetic field, an armature-coil in a neutral locationin thefield, a telephonic transmitter, and con-,

nections arranged with relation to the reciprocal effects of the coiland magnetic field to impart mechanical vibrations perpendicularly tothe receiving member of the transmitter.

6. In an instrument for repeating electrical undulations, thecombination of a magnetic field, an armature-coil in a neutral locationin the field wound so that the mechanical vibrations due to thereciprocal magnetic effects of the coil and field are rectilinear, atelephonic transmitter, and connections to impart thereto the saidrectilinear mechanical vibrations.

7 In an instrument for repeating electrical undulations, the combinationof a magnetic field, an armature-coil in a position of balance therein,a telephonic transmitter, and a stem rigidly connecting thearmature-coil with the receiving member of the transmitter.

8. In an instrument for repeating electrical undulations, thecombination of a magnetic field, an armature-coil in a neutral locationin the field, a telephonic transmitter and astem rigidly connecting thearmature-coil with the receiving member of the transmitter.

9. In an instrument for repeating electrical undulations, thecombination of a magnetic field, an armature-coil in a positlon ofbalance therein, a transmitter, a stem fixed to the undulations, thecombination of a magnetic field, an armature-coil therein, a telephonictransmitter, a mounting for the armature secured to the transmitter atone side and on a support at the other side.

11. In an instrument for repeating electrical undulations, thecombination of a magnetic field, an armature-coil therein, a telephonetransmitter at one side of the armature, a diaphragm at the other, and amounting for the armature secured at one end to the transmitter and atthe other to the diaphragm.

12. In an instrument for repeating electrical undulations,thecombination of a pair of horseshoe-magnets arranged with their similarpoles in diagonal opposition, an armature-coil in neutral location inthe field of the said magnets, a transmitter, connections between thetransmitter and armature-coil, the coil wound with relation to the fieldto impart rectilinear vibrations to the transmitter.

13. In an instrument for repeating electrical undulations, thecombination of a pair of horseshoe-magnets arranged with their similarpoles in diagonal opposition, an armature-coil in neutral location inthe field of the said magnets, a transmitter on one side of the coil anda support on the other, and a stem holding the armature, and connectedwith the transmitter and the support.

14. In an instrument for repeating electrical undulations, thecombination of a pair of horseshoe-magnets arranged with their similarpoles in diagonal opposition, an armature-coil in neutral location inthe field of the said magnets, a transmitter on one side of the coil anda diaphragm on the other and a stem holding the armature,secured to thetransmitter and to the diaphragm.

15. In a telephone system, two telephonelines, a pair of relayinstruments whereof the principal parts are a microphonic transmitter,an armature-coil connected to the transmitter, and a magnetic fieldsurrounding the armaturecoil, each of the two telephone-lines branchedto include the armature-coil of one relay in one branch and thetransmitter of that relay in the other branch inductively.

16. In a telephone system, in combination, a battery-circuit, a batterytherein; two induction coils, each having its primary arranged in saidcircuit, two transmitters in said circuit, two magnetic fields one foreach transmitter; two armature-coils one in each field and eachcontrolling the transmitter of its respective field; twotelephone-circuits each including one of said armature-coils and alsothe secondary of one of the induction-coils.

17. In a telephone system, in combination, a battery-circuit; a batterytherein; two induction-coils each having its primary arranged in saidcircuit; two transmitters in said circuit; two magnetic fields one foreach transmitter; two normally balanced armature-coils one in each fieldand each of said coils arranged to control one of the transmitters andtwo telephone-circuits each including one of said armature-coils andalso the secondary of one of the induction-coils.

18. In a telephone system in combination, a battery-circuit; a batterytherein; two inductiOn-coils each having its primary arranged in saidcircuit; two transmitters in said circuit; two magnetic fields one foreach transmitter; two normally balanced armatures, one in each fieldeach of said armatures being provided with an armature-coil and arrangedto control one of the transmitters, and two telephonecircuits eachincluding one of said armaturecoils and also the secondary of one of theinduction-coils.

Signed by me, at Boston, Suffolk county,

' Massachusetts, this 5th day of May, 1903.

JOHN TROWBRIDGE.

Witnesses:

ODIN ROBERTS, ARTHUR F. RANDALL.

